The functional group would be the aromatic ring.
Functional groups in organic compounds are a group of atoms that gives the compound a distinctive chemical property or properties.
The major functional groups include Hydroxyl, sulfhydryl, carbonyl, carboxyl, amino, and phosphate groups. Aromatic rings are also considered a functional group.
Functional groups are made up of atoms of elements that are covalently linked to each other. The functional group as a whole is also covalently linked to the rest of the molecule.
Functional groups influence molecules to behave in a particular way when it comes to chemical reactions.
Looking at the image (see the attached), none of the side chains qualify as functional groups except the mother chain which is an aromatic ring.
Thus, the only functional group remains the aromatic ring.
More on functional groups can be found here: https://brainly.com/question/14618322
#SPJ1